The enzymatic characterization of peroxisomes from liver, kidney and other tissues of the body continues. More work will be done with liver peroxisomes from mice because nearly 100% recovery of intact particles can be obtained in contrast to only 25 to 40% recovery from rats. Previous research on the effect of Clofibrate on peroxisomal enzyme activity will be reduced for lack of personnel, but other projects will deal with comparisons of the level of peroxisomal enzymes in normal and obese strains of mice and postnatal development in these two phenotypes. Fatty acid beta oxidation in liver peroxisomes of mice is very active and stable, which will facilitate studies of the role of peroxisomes in liver and kidney. Efforts will continue to isolate and identify factors which stimulate peroxisomal glycerol phosphate oxidation as measured by NAD reduction and by oxygen uptake. The location of several other enzymatic activities previously thought to be in the cytoplasm are being investigated in the peroxisomes.